Function.prototype.myCall=function(...arg){
    let self = arg.shift()
    const fn = Symbol()
    self[fn]=this
    return self[fn](arg)
}

let a ={
     name : 'xiaoxian',
     getName : function(){
        console.log(this.name);
     } 
}
let b = {
    name : 'xiaodeng'
}

a.getName.myCall(b)